1. Field of the Invention
This invention lies in the field of gaseous fuel burners. More particularly, it concerns the design of a burner system which can burn gaseous fuels with a minimum quantity of NOx.
More particularly, it is concerned with a type of burner system in which the production of NOx is minimized.
2. Description of the Prior Art
Generation of oxides of nitrogen (NOx), which are air pollutants of a somewhat serious nature, is a characteristic of all fuels burning. It has been found impossible to completely stop all of the generation of NOx as fuels burn, but it is possible to suppress the production of NOx to a significant degree, in all cases, if the air for combustion is premixed with combustion gases CO.sub.2 and H.sub.2 O prior to combustion. Without the gas combustion products addition to the air supply, the NOx concentration may be hundreds of parts per million (PPM), but with added combustion product gases, the NOx evolved can be brought to less than 100 PPM.
The reduction of NOx is thought to be due to the presence of both, or either, CO.sub.2 and H.sub.2 O in the air, enroute to the combustion zone, to cause typical reactions as follows: EQU CH.sub.4 +CO.sub.2 =2CO+2H.sub.2
and EQU CH.sub.4 +H.sub.2 O=CO+3H.sub.2
through these reactions the combustible partial pressure within the reducing areas of the flame is approximately quadrupled, and NOx generally can supply oxygen for support of combustion, which reduces the NOx presence, as has been related. No better explanation has been advanced for NOx reduction in this manner. However, the problem involved is getting the CO.sub.2 and H.sub.2 O, that is, the products of prior combustion, into the combustion air for introduction into the combustion zone of the principal fuel burning portion of the system.
Cumbersome means have been provided for the recirculation of flue gas from stack back to the burner, so that the products of combustion can be introduced into the combustion air prior to entry into the combustion zone. Such means for recirculation of stack gases is one expedient, but is a very expensive one, since it involves the necessity of conduits and blowers handling hot flue gases, etc. This invention provides the products of a preliminary combustion, upstream of the main gas burner so that the secondary air flowing to the primary burner will carry the products of combustion from the preliminary burner, into the main combustion zone. This provides for burning a small part of the gaseous fuel upstream of the main burner in such a way that the heat of combustion of the preliminary burner is combined with that of the main burner, and no heat is lost, while products of combustion from the preliminary burner are utilized in the main combustion zone to minimize NOx production.